1. Sulfur in Hydrocarbons
Elemental sulfur and sulfur compounds are naturally present in crude petroleum. The amount of sulfur varies over a wide range; for example, crude petroleum from West Texas contains about 0.2 weight percent sulfur whereas crude petroleum from Saudi Arabia contains about 5.0 weight percent sulfur. The types of sulfur compounds present in the crude also exhibit a wide variety. These compounds range from hydrogen sulfide, which is a gas at room temperature, to heavy sulfur compounds which boil at over 1000.degree. F.
When crude petroleum is processed in an oil refinery, one of the first steps is to separate the crude into various fractions based on boiling points. The unit used for this separation is a distillation column operated at atmospheric pressure and commonly called the crude still. The separation of the hydrocarbons also separates the sulfur compounds so that the lower-boiling hydrocarbons contain lower-boiling sulfur compounds and higher-boiling hydrocarbons contain higher-boiling sulfur compounds.